Apparatuses and methods to enhance passivation and ILD reliability

ABSTRACT

Some embodiments of the present invention include apparatuses and methods relating to processing and packaging microelectronic devices that reduce stresses on and limit or eliminate crack propagation in the devices.

TECHNICAL FIELD

Embodiments of the invention relate to semiconductor processing andpackaging technology. In particular, embodiments of the invention relateto enhancing passivation and interlayer dielectric reliability.

BACKGROUND

In the production of microelectronic products, a microelectronic chip ordie is typically packaged before it is sold. The package may provideelectrical connection to the chip's internal circuitry, protection fromthe external environment, and heat dissipation. In one package system, achip may be flip-chip connected to a substrate. In a flip-chip package,electrical leads on the die are distributed on its active surface andthe active surface is electrically connected to corresponding leads on asubstrate.

FIGS. 1A-1D illustrate a prior art method for producing and packaging amicroelectronic chip or die. FIG. 1A illustrates a die 100 including asubstrate 105, a device region 110, an interconnect region 115, a bondpad 120, a passivation layer 125, a barrier metal 130, and a bump 140.Interconnect region 115 includes a plurality of metal interconnectlayers that interconnect the devices of device region 110 and provideelectrical routing to external circuitry. The metal interconnect layersinclude metal traces separated and insulated by an interlayer dielectric(ILD) material. Adjacent metal interconnect layers are typicallyconnected by vias which are also separated and insulated by an ILD.

FIG. 1A also illustrates an undercut 135. Undercut 135 may result from abarrier metal layer etch in the presence of bump 140 which etches alayer of barrier metal material from passivation layer 125 and leavesbarrier metal 130. Undercut 135 provides a location for the formation ofundesired cracks in passivation layer 125 and/or interconnect region115. For example, undercut 135 may cause a first crack in passivationlayer 125 which subsequently causes an additional crack or cracks in theILD of interconnect region 115. The subsequent cracks may be connectedto the initial crack or they may be disconnected from, but related to,the initial crack. In particular, low dielectric constant (low-k) ILDmaterials are typically susceptible to cracks. The cracks in passivationlayer 125 and/or interconnect region 115 may cause poor performance orfailure of die 100.

Further, even in the absence of an undercut, bump 140 and the corners ofbump 140 near passivation layer 125 are typically causes of undesiredcracking and stress in passivation layer 125 and the ILD of interconnectregion 115.

In FIGS. 1B and 1C, die 100 is flip-chip bonded to a substrate 180 whichincludes bumps 190. In bonding die 100 and substrate 180, stresses aretypically imparted on die 100 due to coefficient of thermal expansionmismatches between die 100 and substrate 180, and other causes. Thesestresses may cause additional opportunity for cracking in passivationlayer 125 and/or interconnect region 115. Further, after die attach andduring “sit” time prior to further processing, cracks may continue topropagate in passivation layer 125 and/or interconnect region 1 15. InFIG. 1D, an underfill 195 is formed between die 100 and substrate 180.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is illustrated by way of example and not by way oflimitation in the figures of the accompanying drawings, in which thelike references indicate similar elements and in which:

FIGS. 1A-1D are cross-sectional views of a prior art method includingflip-chip attaching a die to a substrate.

FIG. 2A is a cross-sectional view of partially formed wafer or dieincluding a device region, an interconnect region, a bond pad, a barriermetal, a bump, and a passivation layer.

FIG. 2B is a view similar to FIG. 2A with a layer over the bump and thepassivation layer.

FIG. 2C is a view similar to FIG. 2B with a portion of the layer removedto form a sidewall structure.

FIG. 2D is a cross sectional view of a substrate including bumps andsidewall structures being flip-chip attached to a substrate includingcontacts.

FIG. 2E is a view similar to FIG. 2D with the substrates attached and anunderfill between them.

FIG. 3A is a cross-sectional view of partially formed wafer or dieincluding a device region, an interconnect region, a bond pad, andpassivation layer.

FIG. 3B is a view similar to FIG. 3A with a portion of the passivationlayer removed to expose the bond pad.

FIG. 3C is a view similar to FIG. 3B with a barrier metal formed overthe bond pad.

FIG. 3D is a view similar to FIG. 3C with a layer formed over thebarrier metal and the passivation layer.

FIG. 3E is a view similar to FIG. 3D with a portion of the layer removedto expose the barrier metal.

FIG. 3F is a view similar to FIG. 3E with a bump formed over the barriermetal.

FIG. 3G is a cross sectional view of a substrate including bumps and alayer among the bumps being flip-chip attached to a substrate includingcontacts.

FIG. 3H is a view similar to FIG. 3G with the substrates attached and anunderfill between them.

FIG. 4A is a cross-sectional view of partially formed wafer or dieincluding a device region, an interconnect region, a bond pad, a barriermetal, a plurality of bumps, and a passivation layer, and a fixture overthe bumps.

FIG. 4B is a view similar to FIG. 4A with a material between thepassivation layer and the fixture and around the bumps.

FIG. 4C is a view similar to FIG. 4B with the fixture removed.

FIG. 4D is a cross sectional view of a substrate including bumps and amaterial around the bumps being flip-chip attached to a substrateincluding contacts.

FIG. 4E is a view similar to FIG. 4D with the substrates attached and anunderfill between them.

DETAILED DESCRIPTION

In various embodiments, apparatuses and methods relating tomicroelectronics processing and packaging are described with referenceto figures wherein the same reference numbers are used to describesimilar elements. However, various embodiments may be practiced withoutone or more of the specific details, or with other methods, materials,or components. In other instances, well-known structures, materials, oroperations are not shown or described in detail to avoid obscuringaspects of various embodiments of the invention. Similarly, for purposesof explanation, specific numbers, materials, and configurations are setforth in order to provide a thorough understanding of the invention.Nevertheless, the invention may be practiced without specific details.Furthermore, it is understood that the various embodiments shown in thefigures are illustrative representations and are not necessarily drawnto scale.

In processing and packaging microelectronic devices, it may be desirableto limit or eliminate cracking in the passivation layer of the device orthe interlayer dielectric (ILD) of the interconnect region of thedevice. Further, it may be desirable to reduce the amount of stress onthe passivation layer or the ILD while attaching the device to asubstrate. Limiting or eliminating cracking and reducing the stresses onthe passivation layer or ILD may reduce the probability of failures inthe device, particularly when low-k ILD materials are used. Further,reducing stresses may enable the use of lead-free materials to attachthe device to packaging substrates, as is further discussed below.Briefly, the present invention may provide structures and methods thatreduce stresses on and limit or eliminate cracking in the passivationlayer or the ILD of a microelectronic device.

FIGS. 2A-2E illustrate methods and apparatuses that may reduce stresseson and limit or eliminate cracking in the passivation layer or the ILDof a microelectronic device.

FIG. 2A illustrates a portion of a microelectronic device 200. Invarious embodiments, microelectronic device 200 may be a wafer or a die.Microelectronic device 200 may include a substrate 205, a device region210, an interconnect region 215, a bond pad 220, a passivation layer225, a barrier metal 230, and a bump 240. In some embodiments,microelectronic device 200 may also include an undercut 235. In anembodiment, microelectronic device 200 may include a plurality of bondpads, barrier metals, and bumps analogous to those shown in FIG. 2A.

Substrate 205 may include any suitable material or materials such assilicon, germanium, gallium arsenide, indium phosphide, silicon oninsulator, or the like. Device region 210 may include any suitabledevices. In an embodiment, device region 210 may include transistors. Inother embodiments, device region 210 may include resistors orconductors. Interconnect region 215 may include a stack of metallizationlayers including metal interconnects separated and insulated by an ILDmaterial or materials. In an embodiment, the ILD may include a low-kILD, having a dielectric constant, k, of less than about 4. Themetallization layers of interconnect region 215 may be electricallyinterconnected to adjacent metallization layers by vias. The vias may beseparated and insulated by an ILD material or materials. In anembodiment, the ILD may include a low-k ILD. In various embodiments,interconnect region 215 may include about 5 to 9 metallization layersand corresponding via layers, although any number of metallizationlayers may be used.

Bond pad 220 may be any suitable material and size. In an embodiment,bond pad 220 may be a portion of a metallization layer of interconnectregion 215. In an embodiment, bond pad 220 may include copper.Passivation layer 225 may include any suitable material. In anembodiment, passivation layer 225 may include a spark passivationmaterial. In another embodiment, passivation layer 225 may include apolyimide material. In an embodiment, passivation layer 225 may surroundbond pad 220 and expose bond pad 220 for barrier metal 230. In anotherembodiment (not shown), bond pad 220 may be surrounded by an adjacentand substantially coplanar ILD material, and passivation layer 225 maybe over the ILD material and expose bond pad 220 for barrier metal 230.

Barrier metal 230 may include any conductive material or stack ofconductive materials. Bump 240 may also include any conductive materialor materials. In an embodiment, bump 240 may include copper. Undercut235 may be of any size or shape, and may be a source for increasedstress and undesirable crack formation and propagation in passivationlayer 225 and interconnect region 215. In an embodiment, undercut 235may not be present.

As illustrated in FIG. 2B, a layer 245 may be formed over passivationlayer 225 and bump 240. Layer 245 may be any suitable material ormaterials. In an embodiment, layer 245 may be a conformal layer. In anembodiment, layer 245 may include silicon nitride. In an embodiment,layer 245 may be a conformal layer formed by chemical vapor deposition(CVD). In another embodiment, layer 245 may be a conformal layer havinga thickness in the range of about 1 to 15 microns. In an embodiment,layer 245 may be a conformal layer having a thickness in the range ofabout 4 to 10 microns. In another embodiment, layer 245 may be aconformal layer having a thickness in the range of about 5 to 15microns.

As illustrated in FIG. 2C, portions of layer 245 may be removed to formstructure 250. Structure 250 may be formed by any suitable technique. Inan embodiment, structure 250 may be formed by an anisotropic etch oflayer 245. In another embodiment, structure 250 may be formed by ananisotropic ion beam etch of layer 245. In an embodiment, layer 245 maybe entirely removed from the top surface of bump 240. In an embodiment,the portion of layer 245 that does not form structure 250 may beentirely removed. However, in some embodiments, a portion or part oflayer 245 that does not form structure 250, such as a thin remnant oflayer 245 or residuals of layer 245, may remain on passivation layer225. Further, in some embodiments, there may be a plurality of bumps andsidewall structures analogous to those shown in FIG. 2C. Betweenadjacent sidewall structures, there may be a gap that exposes theportion of passivation layer 225 between the adjacent sidewallstructures.

In an embodiment, structure 250 may be around the sides of bump 240 andmay therefore be referred to as a sidewall structure. In an embodiment,structure 250 may surround bump 240. In an embodiment, structure 250 mayhave about the same height as bump 240. In other embodiments, structure250 may have a height that is less than the height of bump 240.Structure 250 may have any suitable width. In an embodiment, structure250 may have a width in the range of about 1 to 15 microns. In anotherembodiment, structure 250 may have a width in the range of about 4 to 10microns. In an embodiment, structure 250 may have a width in the rangeof about 5 to 15 microns.

Structure 250 may limit or eliminate the formation and propagation ofcracks in passivation layer 225 or the ILD of interconnect region 215.Also, structure 250 may lower the stress on passivation layer 225 andthe ILD of interconnect region 215. In an embodiment, structure 250 maylimit or eliminate cracks and lower the stresses on passivation layer225 and the ILD of interconnect region 215 by encapsulating undercut235. In another embodiment, structure 250 may limit or eliminate cracksand lower the stresses on passivation layer 225 and the ILD ofinterconnect region 215 by providing load sharing with bump 240. In anembodiment, structure 250 may lower the stress on passivation layer 225and the ILD of interconnect region 215 during subsequent processing,such as die attach.

As illustrated in FIGS. 2D and 2E, device 200 may be attached to asubstrate 280 including contacts 290; and an underfill 295 may be formedbetween device 200 and substrate 280. In FIGS. 2D and 2E, some detailsof FIG. 2C are not shown for the sake of clarity.

In an embodiment, the formation of structure 250 may be at or near theend of wafer processing and the attachment of device 200 and substrate280 may be performed after dicing substrate 205. In an embodiment,attaching device 200 and substrate. 280 may include a flip-chipattachment. In an embodiment, attaching device 200 and substrate 280 mayinclude a reflow process. In an embodiment, underfill 295 may include acapillary underfill. In another embodiment, underfill 295 may include ano-flow underfill.

Substrate 280 may be any suitable packaging substrate, such as a printedcircuit board (PCB), interposer, motherboard, card, or the like. In someembodiments, contacts 290 may extend away from the surface of substrate280 and contacts 290 may be considered bumps. In an embodiment, contacts290 may be bumps that include a lead-based solder. In other embodiments,contacts 290 may be bumps that include a lead-free solder. Inparticular, the use of the methods and apparatus described may enablethe use of lead-free solders, which are typically less malleable thanlead-based solders. In an embodiment, contacts 290 may be bumps thatinclude a lead-free solder comprising tin, silver, or indium.

FIGS. 3A-3H illustrate methods and apparatuses that may reduce stresseson and limit or eliminate cracking in the passivation layer or the ILDof a microelectronic device.

FIG. 3A illustrates a portion of a microelectronic device 300. Invarious embodiments, microelectronic device 300 may be a wafer or a die.Microelectronic device 300 may include substrate 205, device region 210,interconnect region 215, bond pad 220, and passivation layer 305.

Passivation layer 305 may include any suitable material. In anembodiment, passivation layer 305 may include a spark passivationmaterial. In another embodiment, passivation layer 305 may include apolyimide material. In an embodiment, passivation layer 305 may surroundand cover bond pad 220. In another embodiment (not shown), bond pad 220may be surrounded by an adjacent and substantially coplanar ILDmaterial, and passivation layer 305 may be over the ILD material andbond pad 220.

As illustrated in FIG. 3B, an opening 310 may be formed to expose bondpad 220. In an embodiment, a portion of bond pad 220 may be exposed. Inan embodiment, the entire top surface of bond pad 220 may be exposed.Opening 310 may be formed by any available technique. In an embodiment,opening 310 may be formed by lithography and etch steps.

As illustrated in FIG. 3C, a barrier metal 315 may be formed. In anembodiment, barrier metal 315 may be formed over bond pad 220 and aportion of passivation layer 305. In another embodiment, barrier metal315 may be formed only over bond pad 220. Barrier metal 315 may includeany suitable material or stack of materials, and may be formed by anysuitable technique. In an embodiment, barrier metal 315 may be formed bydeposition, lithography and etch techniques.

As illustrated in FIG. 3D, a layer 320 may be formed over barrier metal315 and passivation layer 305. Layer 320 may be any suitable materialand may be formed by any suitable technique. In an embodiment, layer 320may include a passivation material. In an embodiment, layer 320 mayinclude a spark passivation material. In another embodiment, layer 320may include a polyimide material. In an embodiment, layer 320 mayinclude a photoresist. In an embodiment, layer 320 may be formed by aspin on technique.

As illustrated in FIG. 3E, an opening 325 may be formed to exposebarrier metal 315. In an embodiment, a portion of barrier metal 315 maybe exposed. In another embodiment, the entire top surface of barriermetal 315 may be exposed. Opening 320 may be formed by any availabletechnique. In an embodiment, opening 320 may be formed by lithographyand etch techniques.

As illustrated in FIG. 3F, a bump 330 may be formed over barrier metal315. Bump 330 may include any suitable material and may be formed by anysuitable technique. In an embodiment, bump 330 may include copper. In anembodiment, bump 330 may be formed by electroplating. In an embodiment,bump 330 may have a height that extends above the height of layer 320.In another embodiment, bump 330 may have a height that is about coplanarwith the height of layer 320.

Layer 320 may limit or eliminate the formation and propagation of cracksin passivation layer 305 and the ILD of interconnect region 215. Also,layer 320 may lower the stress on passivation layer 305 and the ILD ofinterconnect region 215. In an embodiment, layer 320 may limit oreliminate cracks and lower the stresses on passivation layer 305 and theILD of interconnect region 215 by providing load sharing with bump 330.In an embodiment, layer 320 may lower the stress on passivation layer305 and the ILD of interconnect region 215 during subsequent processing,such as die attach.

As illustrated in FIGS. 3G and 3H, device 300 may be bonded to substrate280 including contacts 290; and underfill 295 may be formed betweensubstrate 205 and substrate 280. In FIGS. 3G and 3H, some details ofFIG. 3F are not shown for the sake of clarity.

In an embodiment, the formation of layer 320 may be at or near the endof wafer processing and attachment of device 300 and substrate 280 maybe performed after dicing substrate 205. In an embodiment, attachingdevice 300 and substrate 280 may include a flip-chip attachment. In anembodiment, attaching device 300 and substrate 280 may include a reflowprocess. In an embodiment, underfill 295 may include a capillaryunderfill. In another embodiment, underfill 295 may include a no-flowunderfill.

As discussed with reference to FIGS. 2D and 2E, contacts 290 may bebumps that include a lead-free solder such as a solder comprising tin,silver, or indium. In particular, the use of the methods and apparatusdescribed may enable the use of lead-free solders, which are typicallyless malleable than lead-based solders.

FIGS. 4A-4E illustrate methods and apparatuses that may reduce stresseson and limit or eliminate cracking in the passivation layer or the ILDof a microelectronic device.

FIG. 4A illustrates a portion of a microelectronic device 400 and afixture 405. In various embodiments, microelectronic device 400 may be awafer or a die. Microelectronic device 400 may include substrate 205,device region 210, interconnect region 215, bond pad 220, andpassivation layer 225. In some embodiments, microelectronic device 400may also include an undercut 235. Microelectronic device 400 and fixture405 may be put together and held together by any suitable technique.

As illustrated in FIG. 4B, a material 410 may be formed between fixture405 and passivation layer 225, and around bumps 240. Material 410 may beany suitable material and may be formed by any suitable technique. In anembodiment, material 410 may include an underfill material. In anotherembodiment, material 410 may include an epoxy. In an embodiment,material 410 may be injected from the side of fixture 405 andmicroelectronic device 400. In an embodiment, fixture 405 may preventmaterial 410 from covering bumps 240.

As illustrated in FIG. 4C, fixture 405 may be removed to leave material410 over passivation layer 225 and around bumps 240. In an embodiment,material 410 may leave a portion of bumps 240 exposed. In an embodiment,a cure step may be performed to harden material 410.

Material 410 may limit or eliminate the formation and propagation ofcracks in passivation layer 225 and the ILD of interconnect region 215.Also, material 410 may lower the stress on passivation layer 225 and theILD of interconnect region 215. In an embodiment, material 410 may limitor eliminate cracks and lower the stresses on passivation layer 225 andthe ILD of interconnect region 215 by encapsulating undercut 235. Inanother embodiment, material 410 may limit or eliminate cracks and lowerthe stresses on passivation layer 225 and the ILD of interconnect region215 by providing load sharing with bump 240. In an embodiment, material410 may lower the stress on passivation layer 225 and the ILD ofinterconnect region 215 during subsequent processing, such as dieattach.

As illustrated in FIGS. 4D and 4E, device 400 may be bonded to substrate280 including contacts 290, and underfill 295 may be formed betweendevice 400 and substrate 280. In FIGS. 4D and 4E, some details of FIG.4C are not shown for the sake of clarity.

In an embodiment, the formation of material 410 may be at or near theend of wafer processing and attachment of device 400 and substrate 280may be after dicing of substrate 205. In an embodiment, attaching device400 and substrate 280 may include a flip-chip attachment. In anembodiment, attaching device 400 and substrate 280 may include a reflowprocess. In an embodiment, underfill 295 may include a capillaryunderfill. In another embodiment, underfill 295 may include a no-flowunderfill.

As discussed with reference to FIGS. 2D and 2E, contacts 290 may bebumps that include a lead-free solder such as a solder comprising tin,silver, or indium. In particular, the use of the methods and apparatusdescribed may enable the use of lead-free solders, which are typicallyless malleable than lead-based solders.

Reference throughout this specification to “one embodiment” or “anembodiment” means that a particular feature, structure, material, orcharacteristic described in connection with the embodiment is includedin at least one embodiment of the invention. Thus, the appearances ofthe phrases “in one embodiment” or “in an embodiment” in various placesthroughout this specification are not necessarily referring to the sameembodiment of the invention. Furthermore, the particular features,structures, materials, or characteristics may be combined in anysuitable manner in one or more embodiments.

It is to be understood that the above description is intended to beillustrative, and not restrictive. Many other embodiments will beapparent to those of ordinary skill in the art upon reviewing the abovedescription. The scope of the invention should, therefore, be determinedwith reference to the appended claims, along with the full scope ofequivalents to which such claims are entitled.

1. An apparatus comprising: a first bump and a second bump on a surface of a substrate; a first sidewall structure adjacent to the first bump and on the surface; a second sidewall structure adjacent to the second bump and on the surface; and a gap between the first sidewall structure and the second sidewall structure that exposes at least a portion of the substrate surface.
 2. The apparatus of claim 1, wherein the substrate comprises a device region and an interconnect region, the interconnect region including a low-k interlayer dielectric material.
 3. The apparatus of claim 1, further comprising: an undercut between the first bump and the surface, wherein the undercut is encapsulated by the first sidewall structure.
 4. The apparatus of claim 1, wherein the first sidewall structure has a width in the range of about 1 to 15 microns.
 5. The apparatus of claim 1, wherein the first sidewall structure comprises silicon nitride.
 6. The apparatus of claim 1, wherein the first bump comprises copper.
 7. The apparatus of claim 1, further comprising: a contact on a second substrate, wherein the first bump and the contact are electrically connected.
 8. The apparatus of claim 7, wherein the contact comprises a third bump including tin and silver.
 9. An apparatus comprising: a substrate including a bond pad; a passivation layer on the substrate, wherein the passivation layer exposes at least a portion of the bond pad; a barrier metal on the bond pad; a bump on the barrier metal; and a second passivation layer on the passivation layer and adjacent to the bump, wherein the second passivation layer exposes a portion of the bump.
 10. The apparatus of claim 9, wherein the substrate includes a device region and a metallization region, the metallization region including a low-k interlayer dielectric material.
 11. The apparatus of claim 9, wherein the second passivation layer comprises a spark passivation layer.
 12. The apparatus of claim 9, wherein the height of the bump extends beyond the height of the second passivation layer.
 13. A method comprising: forming a bump on a surface of a substrate; forming a conformal coating over the bump and the surface; and removing a portion of the conformal coating to expose a portion of the bump and to form a sidewall structure adjacent to the bump and on the surface.
 14. The method of claim 13, wherein removing the portion of the conformal coating comprises an anisotropic etch.
 15. The method of claim 13, further comprising: flip-chip mounting the substrate to a second substrate having a second bump.
 16. The method of claim 13, wherein the sidewall structure has a width in the range of about 1 to 15 microns.
 17. The method of claim 13, wherein removing the portion of the conformal coating exposes a portion of the surface.
 18. A method comprising: forming a passivation layer over a substrate including a bond pad; removing a portion of the passivation layer to expose at least a portion of the bond pad; forming a barrier metal over the bond pad; forming a layer over the passivation layer and the barrier metal; removing a portion of the layer to expose at least a portion of the barrier metal; and forming a bump over the barrier metal.
 19. The method of claim 18, wherein forming the bump comprises electroplating.
 20. The method of claim 18, wherein removing the portion of the passivation layer comprises a lithography step and an etch step.
 21. The method of claim 18, further comprising: attaching the substrate to a second substrate including a contact, wherein the bump and the contact are electrically connected.
 22. A method for reducing crack propagation from barrier metallization layer undercut in a bumped substrate comprising: securing a fixture to a plurality of bumps on a surface of the bumped substrate; forming a material between the surface and the fixture; removing the fixture; attaching the substrate to a second substrate having a plurality of contacts, wherein at least one bump and at least one contact are electrically connected.
 23. The method of claim 22, wherein the material comprises an epoxy.
 24. The method of claim 22, wherein the material comprises an underfill material.
 25. The method of claim 24, further comprising: curing the underfill material. 